The present invention relates to a lead(Pb)-free sliding material comprising polytetrafluoroethylene resin as the main components for use, for example, as a plain bearing material.
Now available are such plain bearing materials with a porous bronze layer on the surface side of steel back metal, in which the porous bronze layer is impregnated with a sliding material comprising a synthetic resin as the main component. Sliding materials comprising polytetrafluoroethylene resin (which will be hereinafter referred to as “PTFE”), which contains about 20 vol. % of lead (Pb) particles, are known as sliding materials of such a kind (as disclosed in e.g. JP-B-39(1964)-16950). Such sliding materials are distinguished in the sliding characteristics, because a low coefficient of friction can be obtained by the inclusion of Pb particles.
However, sliding materials free from Pb have been keenly desired from the viewpoint of the recent environmental or ecological problems, even if the sliding materials are those comprising PTFE as the main component, as mentioned above. The present inventor has already invented sliding materials containing bismuth (Bi) particles or bismuth alloy particles in place of the conventional Pb and has filed a patent application (Japanese Patent Application No. 2000-26671), where Bi can effectively work as a substitute for Pb particularly to show a catalytic action to form a PTFE coating film (as transferred onto the surface of a counterpart material in the same manner as Pb), and thus stable sliding characteristics can be obtained. However, even such sliding materials comprising Bi or Bi alloy-containing PTFE as mentioned above still have a room for improvement as to the wear resistance. That is, further improvement of wear resistance has been still now keenly desired.